One application of such breathing masks is represented by so-called CPAP (continuous positive airway pressure) respirators. Patients who require respiratory support for various reasons, for example, sleep apnea or COPD (chronic obstructive pulmonary disease), are frequently treated with such CPAP respirators. A settable overpressure is now made available to the patient for supporting the respiration. The supply is usually with constant pressure over the entire breathing cycle, the set pressure being made available via a breathing mask. These breathing masks are usually designed as nose or mouth-and-nose masks, which are connected, for supplying the breathing mask, with flexible tubes, via which they are supplied from a CPAP respirator. The expired breathing air usually escapes through an expiration valve, which is frequently integrated within the mask. In addition, a humidifier or a combined heat/moisture exchanger is frequently present.
Since the diseases treated with such breathing masks are often illnesses that are underestimated by the patients affected, it is important for a successful therapy that the devices to be used, including the breathing masks, find sufficient acceptance by the users in order to be used regularly. However, the wearing of breathing masks is usually linked with negative associations and is felt to be highly uncomfortable. The wearing of a breathing mask seems to be an expression of being in need of help because of an already manifest disease. The putting on of the mask by means of a strap and the use of separate flexible tubes for feeding the breathing gas from the respirator or CPAP respirator to the breathing mask creates a highly technical mechanical impression. Moreover, the feed via the flexible tube frequently takes place via the patient's forehead, which can be felt as an accentuation of the manifestation of being dependent on a machine and, moreover, it greatly compromises recognizability in a facial area that determines the facial expressions. The disfigurement seemingly associated with the therapy even leads to rejection of such a therapy in extreme cases. Another problem in the acceptance of prior-art breathing masks is the nuisance associated with the generation of noise during expiration, which is due to the model of the breathing mask. The expiration valve usually comprises a simple hole, which is arranged directly in the mask or in the immediate vicinity of the mask, or a plurality of openings, which may be complicated. A gas flow corresponding to the overpressure being provided is continuously escaping from these openings into the environment. The use of individual holes as an expiration valve in or on CPAP masks leads to a locally occurring, high velocity of flow in the immediate vicinity of these holes. This high velocity of flow turns the expiration valve into a disturbing source of noise.
Besides the generation of noise, the focusing of escaping gas flows represents an additional drawback. A gas flow hitting the surfaces of the face, especially in the area of the patient's eyes, may be usually felt to be highly unpleasant and may lead to complaints, especially in the area of the eyes.
The amount of gas that can be discharged from the discharge valves is determined essentially by the flow resistance of the discharge valves. On the one hand, the amount of gas should be as small as possible in order to keep possible nuisances in terms of the generation of noise and the draft resulting from focused gas flows as low as possible. On the other hand, a minimum permeability is necessary, because no appreciable increase in pressure is to take place in the area of the mask during the expiration by the patient, which takes place against the constant pressure being provided anyway. If a great increase in pressure is to be avoided during expiration, it is, moreover, desirable not to allow the velocities of flow to rise above a point at which changeover of the laminar flow into a turbulent flow takes place. There is only a linear increase in the volume flow with the existing pressure difference in the laminar flow range. This dependence no longer applies if there is a changeover into a turbulent flow with increasing velocity of flow. There will now be a very rapid pressure rise even during a slight further increase in the volume flow through the expiration valves, because the flow resistance increases greatly. This increasing pneumatic resistance is felt by the patient to be very unpleasant. It is therefore known that the expiration valve should be designed as an array of many small discharge openings. As a result, the volume flow being discharged is divided into many individual flows, and only low velocities of flow are reached even in case of large volume flows that pass through the expiration valve. However, such valves are additional complex components and they frequently cannot be mounted directly on the mask and, moreover, they produce an additional dead space. Moreover, they promote condensation when a humidifier is used, as a result of which their pneumatic properties may change.